Intaglio printing machines are known in the prior art, especially for the printing of securities such as bank-notes and other similar objects. For example, U.S. Pat. No. 5,062,359, the content of which is enclosed by reference in the present application, discloses a sheet-fed or web-fed intaglio printing machine. This machine comprises a plate cylinder with several printing plates, an impression cylinder, a wiping device and an inking system with a collector inking cylinder, having an elastic surface, interacting with the printing plates, with selective inking cylinders having reliefs corresponding to the coloured zones to be printed in different colours and in contact with the periphery of the collector inking cylinder, and of an inking device associated with each selective colour inking cylinder.
Another machine is disclosed for example in U.S. Pat. No. 4,516,496, the content of which is enclosed by reference in the present application. This patent also discloses an intaglio printing machine similar to the one of U.S. Pat. No. 5,062,359 mentioned above. As shown in this patent, the inking system comprises a plurality of selector cylinders which are used for transferring the ink in a given colour from the inking units onto the collector cylinder, which in turn inks the engravings of the plates. Each selector cylinder has a hard surface, for example surfaces lined with hardened rubber, plastic or the like, or metal, each selector cylinder comprising relief areas having contours corresponding exactly to the contours of the surface to be printed with the corresponding colour.
Another example of an intaglio printing machine is disclosed in U.S. Pat. No. 5,899,145, the content of which is enclosed by reference in the present application.
A problem which is present in this field resides in the fact that the inking of the intaglio structure, in particular of the plates is not precise, therefore ink is transferred on a larger area than the effective intaglio structure, this ink being later wiped away by the wiping system. Accordingly, a high quantity of ink is lost because it is deposited outside the places effectively corresponding to engravings of the plates, and is then wiped away without being used for inking the plates.
Another problem one is faced with in this printing technique is the fact that, due to the high pressure necessary for the printing operation, the plates undergo an elongation deformation over their lifetime which is then prejudicial to the perfect register between the blankets of the collector cylinder and the plates with the engravings. For this reason, ink is also deposited outside the engravings and is lost by the wiping operation.
In order to avoid this loss of unused ink, one thus tries to increase the precision of depositing the ink in the engravings of the plates.